1. Field of the Invention
The present invention relates to a method and apparatus for the continuous filtration of material impregnated with liquid.
2. Description of the Prior Art
Different methods and apparatuses are already known for the filtration of various materials, in particular sludges, operating continuously or discontinuously.
In a known filtration apparatus of the continuous type, the material to be filtered is passed between two bands one of which is permeable, these two bands being pressed one against the other under pressure. This method of filtration has the drawback that it is hardly possible to apply a very high pressure to the material to be filtered, since the latter is not enclosed in a sealed chamber and, if the pressure were too high, this would result in lateral leakages. Limitation of the pressure which can be exerted thus causes a correlative limitation of the overall output which can be achieved by the filtration apparatus.
Other filtration apparatus operate discontinuously: the latter are filter presses. These filter presses make it possible to exert a much higher pressure on the material to be filtered than in an apparatus operating continuously, this pressure being able to reach 15 bars. On the other hand, they have a very long cycle time, which may be of the order of 3 hours, this cycle time corresponding to the duration of complete filling of the chambers and to that for undoing or opening the filter, for the purpose of emptying the cake, this operation itself being followed by re-closing of the filter. These apparatuses have the drawback that the opening operation thereof, whether carried out manually or automatically, takes up a major part of the cycle time, during which the filter is not operational and in all cases requires the presence of an operator
From the point of view of dryness (ratio between the weight of dry material and the total weight of the filtered sludge), the continuous method using a band makes it possible to achieve dryness of the order of 25%, whereas a filter press makes it possible to achieve greater dryness, of the order of 40 to 45% for example.